The mechanism of CO2 insertion into iridium(I) hydroxide and alkoxide bonds: a kinetics and computational study.

The facile insertion of CO2 into iridium(I) hydroxide, alkoxide, and amide bonds was recently reported. In particular, [Ir(cod)(IiPr)(OH)] (IiPr = 1,3-bis(isopropyl)imidazol-2-ylidene) reacted with CO2 in solution and in the solid state in a matter of minutes to give the novel [{Ir(cod)(IiPr)}2(µ-κ(1)O:κ(2)O,O-CO3)] complex. In the present study, this reaction is probed using kinetics and theoretical studies, which enabled us to analyse its facile nature and to fully elucidate the reaction mechanism with excellent correlation between the two methods.

Fluoride, bifluoride and trifluoromethyl complexes of iridium(I) and rhodium(I).

Herein we report robust methods for the preparation and full characterisation of a range of Ir(I) and Rh(I) fluoride and bifluoride complexes using N-heterocyclic carbenes (NHCs) as ancillary ligands. The processes that link the fluoride and the bifluoride species are investigated and reports of the first Ir-bifluoride and Ir(I)-NHC and Rh(I)-NHC trifluoromethyl complexes are revealed.

Iridium(I) hydroxides in catalysis: rearrangement of allylic alcohols to ketones.

The iridium(I) hydroxide complex [Ir(OH)(COD)(I(i)Pr)] has been shown to be a competent catalyst for the rearrangement of allylic alcohols to ketones. Reactions proceed in short reaction times (1-1.5 h) with microwave heating, in the absence of additives.

CO2 fixation employing an iridium(I)-hydroxide complex.

The reactivity of a number of Ir(I) complexes towards CO2 is explored using [Ir(NHC)(OH)] as a key synthon. CO2 insertion into Ir-O and Ir-N bonds proved facile, yielding a number of Ir(I)-carbonates and -carbamates. Most importantly, reaction between CO2 and Ir(I)-OH led to isolation of the novel [{Ir(I)}2-(µ-κ(1):κ(2)-CO3)] complex.

Synthesis and reactivity of new bis(N-heterocyclic carbene) iridium(I) complexes.

New complexes of the type trans-[IrCl(η(2)-COE)(NHC)2] (COE = cis-cyclooctene; NHC = N-heterocyclic carbene) have been prepared in one step from the reaction of ca. 4 equiv of NHC or [AgCl(NHC)] with [IrCl(η(2)-COE)2]2 in benzene. These new complexes have been characterized by techniques including NMR and IR spectroscopy, X-ray crystallography, and elemental analysis. Exposing trans-[IrCl(COE)(I(i)Pr(Me))2] to CO yielded trans-[IrCl(CO)(I(i)Pr(Me))2], which is the only bis(NHC) analogue of Vaska's complex trans-[IrCl(CO)(PPh3)2] known to date. The synthesis of trans-[Ir(CO)(I(i)Pr(Me))2(R)] (R = MeO, PhCC, OSiPh3, O2CPh) complexes has been achieved via deprotonation reactions involving the new hydroxide species trans-[Ir(OH)(CO)(I(i)Pr(Me))2].

Iridium(I) hydroxides: powerful synthons for bond activation.

A family of iridium(I) hydroxides of the form [Ir(cod)(NHC)(OH)] (cod = 1,5-cyclooctadiene, NHC = N-heterocyclic carbene) is reported. Single-crystal X-ray analyses and computational methods were used to explore the structural characteristics and steric properties of these new complexes. The model complex [Ir(cod)(IiPr)(OH)] (IiPr = 1,3-(diisopropyl)imidazol-2-ylidene) undergoes reaction with a wide variety of substrates including boronic acids and silicon compounds. In addition, O-H, N-H and C-H bond activation was achieved with alcohols, carboxylic acids, amines and various sp-, sp(2)- and sp(3)-hybridised carbon centres, giving access to a wide range of new Ir(I) complexes. These studies have allowed us to explore the exciting reactivity of this motif, revealing a versatile and useful synthon capable of activating important chemical bonds under mild (typically room temperature) conditions. No additives were required and, in the case of X-H bond activation, water was the only waste product, rendering this an atom efficient procedure for bond activation. This system has great potential for the construction of new catalytic cycles for organic synthesis and small-molecule activation.

Well-defined NHC-rhodium hydroxide complexes as alkene hydrosilylation and dehydrogenative silylation catalysts.

Alkene hydrosilylation and dehydrogenative silylation reactions, mediated by [Rh(cod)(NHC)(OH)] complexes (cod = 1,5-cyclooctadiene; NHC = N-heterocyclic carbene) are described. The study details a comparison of the catalytic activity and steric characteristics of four rhodium complexes bearing different NHC ligands. The novel [Rh(cod)(Ii-PrMe)(OH)] complex (Ii-PrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidine) was designed to improve the reactivity of Rh(I)-hydroxides and proved to be a successful promoter of hydrosilylation and dehydrogenative silylation, displaying good stereo- and regiocontrol.

Well-defined [Rh(NHC)(OH)] complexes enabling the conjugate addition of arylboronic acids to α,ß-unsaturated ketones.

The synthesis and catalytic activity of three well-defined monomeric rhodium(I) hydroxide complexes bearing N-heterocyclic carbene (NHC) ligands are reported. [Rh(cod)(ICy)(OH)] promoted the 1,4-addition of arylboronic acids to cyclic enones, with TONs and TOFs of 100,000 and 6,600 h(-1), respectively, at 0.001 mol% catalyst loadings. Mechanistic studies permitted the isolation of a phenylrhodium intermediate.